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General Information - Siemens 3TK2845 Manual

Safety relays, multifunction device
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Functional Information
2.1

General Information

SIRIUS safety relays in the safety chain
In general, a safety chain is made up of the three parts detection, evaluation and
switching-off.
Detection: means the detection of a safety requirement, e.g. when someone
activates an EMERGENCY-STOP or enters a hazardous area protected by
sensors such as light grids or laser scanners.
Evaluation: means the detection of a safety requirement and the safe initiation
of the reaction (e.g. switching-off of the enabling circuits).
Switching-off: means the switching-off of the hazard (e.g. of a power supply via
the downstream contactors).
SIRIUS safety relays play a role in the evaluation and reaction part of the safety
chain.
The safety functions are shown in a uniform schematic diagram (refer to
2.2) for a quick overview of the special functions of the individual device types.
The sensor interface inputs, the actuator interface outputs and enabling circuits
as well as the special safety logic can all be seen at a glance.
Cascading input
1. Safe linking of safety devices
In this application a higher-level safety device switches off the 3TK2845 via a
safe output and the cascading input.
Example:
A -- higher-level -- EMERGENCY-STOP circuit must switch off the whole
system.
Several lower-level functional groups (e.g. protective doors) with local switch-off
can be operated.
Notice
If faults can be excluded (protected wiring of the control cable), the application's
safety category is the same as the safety category of the higher-level safety
relay.
2. Additional safety sensor circuit
The cascading input is AND-connected with the sensor inputs Y12, Y22. Safety
category 2 according to EN 954-1 can be achieved when the cascading input is
wired to single-channel safety sensors (positive opening) and the routing of the
connecting cable is protected. The start function is set to automatic start-up.
Cascading input 1 can be switched with floating or electronic switching
elements. Both types of switching elements must be fed by the same power
supply as the device.
3. Operational switching
The cascading input can be used for operational (non-safe) switching. Switching
is possible with floating or electronic switching elements. Floating switching
elements must be fed by the same power supply as the device.
Automatic sensor detection
Sensors such as EMERGENCY-STOP control switches or position switches and
safety mats have different modes of operation. While EMERGENCY-STOP
control switches, for example, interrupt the sensor circuit when activated, safety
2-2
Chapter
3TK2845 Multifunction Device Manual
GWA 4NEB 926 2087-22 DS 01

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